The present invention relates generally to the field of marine surveying. More particularly, in one or more embodiments, this invention relates to rigid protracted geophysical equipment that comprise control surfaces and associated methods of use in marine geophysical surveys.
Techniques for marine surveying include marine geophysical surveying, such as seismic surveying and electromagnetic (“EM”) surveying, in which geophysical data may be collected from below the Earth's surface. Geophysical surveying has applications in mineral and energy exploration and production to help identify locations of hydrocarbon-bearing formations. Certain types of marine geophysical surveying, such as seismic or electromagnetic surveying, may include towing an energy source at a selected depth—typically above the seafloor—in a body of water. One or more geophysical sensor streamers also may be towed in the water at selected depths by the same or a different vessel. The streamers are typically cables that include a plurality of sensors disposed thereon at spaced apart locations along the length of the cable. The sensors may be configured to generate a signal that is related to a parameter being measured by the sensor. At selected times, the energy source may be actuated to generate, for example, seismic or EM energy that travels downwardly into the subsurface rock. Energy that interacts with interfaces, generally at the boundaries between layers of rock formations, may be returned toward the surface and detected by the sensors on the streamers. The detected energy may be used to infer certain properties of the subsurface rock, such as structure, mineral composition and fluid content, thereby providing information useful in the recovery of hydrocarbons.
In geophysical surveying, the geophysical equipment, such as the streamers, are typically cables that are stored on a drum. The streamers are typically made of multiple components, such as electrical conductors, fiber optics, and stress-supporting members, all bundled together and covered with a protective outer skin. The streamer may be up to several kilometers in length. A lead-in is another usual part of geophysical equipment. The lead-in is typically a cable that couples the streamer to the survey vessel and may be stored on a drum, typically the same drum as the streamer. To deploy, retrieve, and store this geophysical equipment, cable-handling systems are typically employed. Such cable-handling systems may include a storage drum in combination with sheaves, blocks, and other turns where a smaller angle of cable direction changes occurs. Drums—often with a smaller diameter—can be used to take off individual sections of the streamer for repair or replacement. In operation, one of the drums is holding back the tension in the deployed cable with its turning moment. In order to avoid load concentration on the cable, it may be beneficial to have many rounds of cable inside the drum while applying force. Thus, the innermost drum, which is the storage drum, is often used to hold back the tension.
The drum causes a number of restrictions and costly features on the geophysical equipment, especially in combination with rigid elements such as connectors, electronics housing, and sensor spacers. For example, the streamer typically should be capable of handling large deformations as a result of storage on the drums, thus limiting the available alternatives for the outer skin of the streamer. Accordingly, options for treating the geophysical equipment for drag reduction and antifouling may be limited. In addition, certain geophysical equipment, such as gel-filled cables, may encounter large, undesired deformations in shape due to storage on the drum, preventing their re-use. For various reasons, some of the components of the geophysical equipment may be external to the cable and attached via connection points to the outside. These external components typically cannot be attached to the cable until the cable is unwound from the drum during deployment. To reduce the complexity associated with this attachment process, there has been an ongoing effort to place these components inside the outer skin of the cable. However, placement of the equipment inside the outer skin is not always practical as adapting a solution for incorporating these components into a cable that is wound onto a drum can be challenging.
In some instances, it may be desirable to control the position of this geophysical equipment, such as lead-ins and streamers, in both the vertical and lateral direction. Control of position may be desirable for a number of reasons, including noise reduction, efficient towing, bin accuracy, and depth/ghost accuracy. Control of rotation of the geophysical equipment may also be useful in some applications. For control of position and/or rotation, wings have been used. Typically, the wings may be mounted on the geophysical equipment at deployment and taken off during retrieval. While the wings may be used for position and/or rotation control, their use may have drawbacks. For example, implantation of wings into the streamers may cause increased noise. In particular, as the streamers may typically be soft, elastic structures, such as cables, the lateral force of the wings may cause streamer deformation generating noise due to crossflow caused by deformations at the intersection of the wings and the streamer. Another drawback that may be associated with wings is exposure to marine growth in the water may cause increased wear and reduce their useful lifespan. Yet another drawback that may be associated with wings is increased crew work load and hazardous operations due to requirement of manual interaction at deployment and retrieval for mounting and removal of the wings. Moreover, additional space may also be required on the vessel for separate wing storage.
Accordingly, there is a need for improved streamers and other seismic equipment that can have position and/or rotation control.